1. Field of the Invention
The present invention relates to an improved process for producing edible quality fish oil. More specifically, the present invention relates to an improved process for producing menhaden fish oil wherein the produced fish oil is edible, retains a high percentage of omega-3 long chain fatty acids, has improved storage stability, and has minimal oxidation.
2. Description of the Related Technology
Certain fish and other marine animals contain oil rich in polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acids (DHA). These fatty acids are referred to as omega-3 fatty acids. The positive health effects of consuming fish oil containing omega-3 fatty acids have been widely reported in recent years (U.S. Pat. No. 5,006,281, issued Apr. 9, 1991 to Rubin et al., U.S. Pat. No. 4,913,921 issued Apr. 3, 1990 to Schroeder et al., and U.S. Pat. No. 4,874,629 issued Oct. 17, 1989 to Chang et al.--incorporated by reference herein). These positive health benefits have been seen in humans and in animals. Unfortunately, untreated fish oils and more specifically fish oils high in omega-3 fatty acid content inherently have an unsavory fish odor and flavor. Furthermore, untreated fish oils high in omega-3 fatty acid are susceptible to oxidation. These fish oils after being oxidized will degrade after a period of hours, and diminish the omega-3 content of the fish oil. However, fish oils high in omega-3 fatty acids can be processed to remove the inherently unsavory fish odor and flavor, and to improve their stability and enhance their storage capability.
Unsavory odors and flavors in fish oils can be initiated by lipid peroxidation catalyzed by enzymatic activity, such as lipoxygenase, peroxidase, and cyclooxygenase. In order to produce an edible fish oil it is important to remove these enzymes and thus remove the unsavory fishy odor and taste from the fish oil.
Fish oil instability and degradation is caused by oxidation and peroxidation of the fatty acids in the fish oil. This is especially true of the omega-3 fatty acids found in oil from menhaden, salmon, sardine, anchovy, and cod. Further oxidation of the fish oil can occur by exposing the fish oil to oxygen, heat, or light.
Numerous processes have been proposed in the past to stabilize fish oils high in omega-3 fatty acids. Some processes involve deodorizing the fish oil by removing the naturally occurring amines present in the fish oil (volatiles) that emanate the "fishy" odor. Deodorizing typically involves steam stripping the fish oil with high temperature steam in a vessel or container to remove the volatiles. This method alone has proven unsuitable since high temperature (above 470.degree. F.) removes or damages the omega-3 fatty acids. As noted above loss of the omega-3 fatty acids eliminates a large portion of the health benefit of the fish oil. Other methods suggested to protect the fish oil against oxidation involve adding anti-oxidants to the oil to protect the oil from subsequent oxidation. Simply adding anti-oxidants to the fish oil has failed to produce an edible fish oil suitable for long term storage since naturally occurring compounds in the fish oil, such as aldehydes, ketones, and carotenoids can seed peroxidation and must be removed to provide antioxidant effectiveness. Each of the aforementioned processes, while having some valuable effect, does little to the inherent oxidative nature of fish oil, and therefore little to improve the long term storage stability of the produced fish oil.
It is therefore desired to develop an improved process for refining an edible fish oil for long term storage such that the oxidative nature of the produced fish oil is reduced, the fish oil is protected against further oxidation, and other impurities in the fish oil are removed. It is imperative that only a small percentage of the omega-3 fatty acids be lost in the refining process. Moreover, the process for refining fish oil should be capable of plant production scale in addition to bench and pilot plant scales, to ensure maximum commercial application.